cant decide which motors to use for 2DOF.

Yes, and i am fully aware of that but i'm guessing i will be okay. when i have all the parts im just going to lay it all out, mount the motors and see what kind of angles the seat will have and how i should mount the wheel to clear everything.
If i find my knees are hitting i will also mount the wheel to the moving frame, But then i still want to have the option to just make it a seatmover, allready have some idea's how to do it so it wont be a problem.
When i was ordering the motors i still had my doubts which motor to take and against to all what ive seen ive picked the 50:1 motors, i figured i could use the extra torque to move my legs and if the motors are to slow in the standard config i could make the levers longer on the motors or connect the rods closer to the center of the seat to give it some more throw.
All in all i think this is going to work nicely because there are plenty of ways to change how this thing is going to react to the smallest motor movements so even with a 10 rpm motor you could make it fly

sounds like a plan

Hey guys, i have a theory and i wanted to hear what some have to say about it before i start to weld the frame and all.

I hope i can make myself clear explaining this because in english it could be a bit harder for me. anyways, he goes:
My theory is that it takes a X amount of force to move a platform (in this case the seat) an X amount of Distance.

lets say we have a seat, mounted on a u-joint and we connect the motors on shoulderheight, in case of this example the height from the u-joint to the mountings on the shoulder is 600mm, the motors have levers on them that are 10cm, this combination makes the seat move with an X amount of force needed at the motors.
Now lets say we decrease the height of the shouldermounts to 300 mm and we also decrease the lever lenght to 5 cm, wouldnt the forces that are needed to move the seat be exactly the same? same goes for the travel the seat makes, it would be identical in both situations? right?
Same goes for where you would place the motors.. 600mm high from the u-joint to the shouldermounts or 600mm towards you feat and between the u-joint, the lever is the same lenght so i\m guessing it must be the same?
Allready tried looking it up in books and on the internet and so far is seems this is exactly the case. will dig a bit deeper into this as i find it very interesting but i was kinda curious what you guys think about it.

hope i made it a bit clear cause like i said its rather difficult to explain it in english

thnxs

Shortening the lever by half will indeed double its torque output. But I think the math is a little more complicated when changing the mounting position to get an exact figure. But lowering it would allow the seat to move further using less input for sure. I know other members here use Sketchup to figure some of this out but I have not used it so I'm not able to help there.

Mounting position of motors is critical when wanting to move a force. Granted a Shoulder mount may have long arms 700mm, but that doesnt mean it takes a lot of power to move them.
Yes @BlazinH lever arm length can reduce torque is too long, but then again @eaorobbie has dc motors shoulder mount 12v 200w 25:1 boxes on them with 65mm CTC lever I think. But because he has set the motors at best leverage point, he only uses a small amount of actual lever on motor travel and throws 120kg driver easy.
I found the lower the mounting, the greater the force needed to move you. Shoulder mount is best at the back. At the front, foot placement mount with motor connections raised up at least above toe level or higher. Shoulders is high above centre of gravity. Foot motors are using wheelbarrow leverage effect.

I agree! When I said, “lowering it would allow the seat to move further using less input” I meant move further using less distance of travel! But the torque would have to be a lot more than if connected higher up! And likely more than double the torque if the mounting position was halved.

I think the forces applied here are similar to the difference between using a short screwdriver and a long screwdriver. If you have ever tried getting a screw loose with a short screwdriver and couldn’t, but switching to a longer screwdriver did the job, you know what I mean! When you are simply twisting a screwdriver or a shaft in other words, it doesn’t seem intuitive that simply making it longer would increase the torque, but it does. But you have to consider not only the screwdriver in the torque equation, but the persons arm that’s twisting it. When you are holding a screwdriver in a screw head, the screwdriver is one leg of a triangle, a person’s arm is the second leg, and connecting an imaginary line between a persons shoulder and the head of the screw is the third. When looked at this way, you can see how changing the length of the screwdriver changes the result!